This invention relates to telephone switching systems. More particularly, this invention relates to a plurality of interconnected PBX switching systems. Still more particularly, this invention relates to a system for providing automated directory look-up over the plurality of interconnected PBX switching systems to find a telephone number for a desired name.
It is common to use Personal Branch exchange (PBX) switching systems to provide telephone services for businesses, dormitories, and other facilities that may have a need for many telephone lines. PBX switching systems allow a business or other place to provide many telephone services to connected telephone sets including but not limited to automated answering, call forwarding, voice mail, and directory look-up. Furthermore, the business may configure their telephone network in any way that the facility desires.
Sometimes a facility may be so large that multiple PBX switching systems are needed to provide telephone service to all of the telephone sets needed in the facility. The use of multiple PBX switching systems causes problems in providing some telephone services. One such telephone service that is problematic when multiple PBX switching systems are used is automated directory look-up.
Automated directory look-up is a problem because each PBX switching system only maintains a record of the telephone numbers assigned to telephone sets connected to the switching system. There is no way for a first switching system to determine whether there is a telephone number associated with a name that is serviced by a second switching system. Therefore there is currently no way to provide automated directory look-up for a business or other facility that is serviced by multiple PBX switching Systems.
The above and other problems are solved and an advance in the art is made by the provision of a system that provides automated directory look-up for a network having multiple switching systems. The present invention allows a calling party that is connected to a first switching system perform an automated directory look-up for a desired name on every switching system in the network. Therefore, a calling party does not have to be connected to the same switching system as a called party to perform a look-up or the telephone number of the called party.
In order to provide automated directory look-up over multiple switching systems, there must be a dedicated Data channel (D-channel) connecting the switching systems in a network. The D-channel is a frequency band or a time division in a frequency band that is transmitted over a dedicated path connecting the switching systems to transmit information between switching systems controllers. Messages are transmitted over the D-channel in a protocol, such as ISDN PRI, which the switching system uses to communicate.
In order to provide automated directory look-up over multiple switching systems in a network, the following process is performed. A request is received by a first switching system for an automated directory look-up. The first switching system then transmits a display or voice message to the telephone set of the calling party, prompting the calling party to input a string of characters representing at least one letter in a name to be found. In the most common embodiment, the characters will be digits that are dialed by the called party where each digit may represent more than one letter of the alphabet.
The first switching system then performs a search for matches to the string of characters in a database of telephone numbers and corresponding names maintained by the first switching system. The first switching system also generates a message requesting a directory look-up from the other switching systems. The request message also includes the string of characters. The request message is transmitted to the other switching systems in the network.
The other switching systems receive the request and perform the following process. First, the other switching systems read the string from the request message. The other switching systems then search for matches in their respective databases of telephone numbers. Each switching systems then generates messages containing the matches. A determination is then made whether or not the switching system has a directory request of its own. If the switching system does have a directory look-up request, the request is transmitted first. The response messages containing matches are then transmitted.
The first switching system receives all of the response messages containing matches from the other switching system. The first switching system maintains a list of all the switching systems that transmit responses with matches. All of the matches are then sorted into some order. Most commonly, this order is alphabetical. The first name is then displayed to the user over a display, such as a Liquid Crystal Display (LCD), in the telephone set or by a voice recording. The user may then determine whether the displayed name is the desired name or scroll through the list of names to find the desired name. If the name is not found, the user may be prompted for additional characters. The additional characters are appended to the end of the string and the process is repeated. In order to reduce traffic over the D-channel, the first switching system may track which other switching systems transmitted matches back to the first switching system and then transmit requests to only those switching systems that transmitted matches.